The feeling, or rather the lack of it that one wishes to fulfill but can never/most of the time seem to get it right.

OR

By the common standards of this website (AKA sexual references everywhere) when you are having a great wank and you feel so f*cking good but the moment after you orgasm, everything is gone (Quite literally).

1]Taken from the song Uzbekistan by The Sound of Animals Fighting:

They're defecting us
They're extracting us
The world owes me nothing, it's given me a great deal
Is this emptiness part of being human?

2]Dan decided that instead of joining his colleagues on a Saturday night, he'd spend his time on his room wanking instead.

As soon as he hit ctrl + shift + n, he typed directly on the browser's url bar the key words: "Kelly Divineanal" and proceeded to produce a monologue whilst touching his genitals.
"-OMG, she's too hot, holy shit, holy fuck, hooooooooooooooooooooooooly...... oh"
After ejaculating, all the temporary excitement seemed to vanish as Dan withered in a strange lack of all the good feelings he was experimenting.
Is this emptiness part of being human?